JP4423791B2 - Piston structure of internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piston structure of an internal combustion engine, and more specifically, a curved shape in which an outer shape of a skirt portion gradually overhangs from an upper end portion to a midway height portion, and the overhang amount gradually decreases from the midway height portion to the lower end portion. It is related with the made piston structure.
[0002]
[Prior art]
If the sliding resistance of the piston is large in an internal combustion engine, the fuel consumption deteriorates due to friction loss, the output decreases, and the durability of the engine deteriorates. Therefore, in order to reduce the sliding resistance of the piston in the internal combustion engine, the outer shape of the skirt part below the piston ring is gradually extended from the upper end part to the middle height part, and the amount of extension is gradually increased from the middle height part to the lower end part. A piston structure having a curved shape (so-called barrel shape) that decreases is conventionally known.
[0003]
For example, a piston skirt shown in Japanese Patent Laid-Open No. 6-185405 has a convex curved portion whose diameter increases (the overhang amount increases) as it goes downward within a predetermined range of the upper portion, and this curved portion And a taper portion below the skirt that decreases in diameter as it goes down to the maximum diameter portion, and the maximum diameter portion is provided in the vicinity of the pin boss center height position. The inclination angle of the taper portion with respect to the piston axis is set to 0.0015 to 0.02 radians in the cold state. In the above publication, as an effect of this configuration, the inclination angle of the taper portion is 0.0015. It is described that sliding resistance is reduced by being more than radians, and that an increase in piston slap noise is suppressed by being 0.02 radians or less.
[0004]
[Problems to be solved by the invention]
However, in the conventional piston structure as described above, it is actually difficult to achieve both reduction of the sliding resistance of the piston and suppression of the slap noise.
[0005]
That is, in the conventional barrel shape as described above, increasing the clearance between the outer periphery of the skirt portion and the inner peripheral wall of the cylinder at the maximum diameter portion is advantageous for reducing sliding resistance. Since the slap noise generated by the swinging motion of the piston in the vicinity tends to increase, it is required to make the clearance as small as possible in order to reduce the slap noise.
[0006]
However, if the clearance is reduced so as to reduce the slap noise to a level that does not cause a problem in the actual vehicle, the sliding resistance increases, and the effect of reducing the sliding resistance due to the barrel shape is negated. In particular, in the conventional barrel shape in which the maximum diameter portion is provided in the vicinity of the pin boss center height position, as will be described in detail later, the upper portion of the skirt is greatly expanded during operation to protrude outward, and the cylinder inner peripheral wall This increases the sliding resistance. For this reason, even if the inclination angle of the tapered portion below the skirt is adjusted as described above, it is difficult to sufficiently reduce the sliding resistance.
[0007]
In view of the above circumstances, the present invention provides a piston structure for an internal combustion engine that can effectively achieve both reduction of sliding resistance and suppression of slap noise even in a state where the upper portion of the skirt is thermally expanded during operation. Is.
[0008]
[Means for Solving the Problems]
According to the present invention, the outer shape of the skirt portion below the piston ring is gradually extended as it goes downward from the upper end portion of the skirt on the piston ring side to the middle height portion, and as it goes downward from the middle height portion to the lower end portion of the skirt. Piston structure of an internal combustion engine in which the overhang amount gradually decreases, and the overhang amount maximum reach height that is the height position where the overhang amount gradually increases and reaches the maximum value as it goes downward from the upper end of the skirt The position is closer to the position of the skirt lower end than the pin boss center height position in the height direction of the piston, and the distance between the protruding amount maximum reach height position and the pin boss center height position is to form a skirt portion outer to the size Kunar such curved shape than the distance between the projecting amount maximum arrival height position as that of the skirt lower end portion, in addition, small In both cases, the cross section at the maximum reach height position of the overhang amount is a compound ellipse shape in which at least two ellipses having a major axis in the thrust / anti-thrust direction perpendicular to the pin boss axis direction and having different flatness ratios are combined. The portions located on both sides in the direction are shaped so that the flatness is small, and the portion located closer to the pin boss than this portion is shaped to have a large flatness .
[0009]
According to this configuration, the skirt upper part becomes larger during operation because the skirt upper part is smaller than the conventional barrel-shaped part where the maximum bulge amount is near the pin boss center height position in the skirt part. Even if it is thermally expanded, the overhang is sufficiently suppressed. Thereby, the reduction effect of the sliding resistance in the vicinity of the top dead center is enhanced. In addition, if the overhang amount of the skirt is reduced in this way, the inclination of the piston in the thrust / anti-thrust direction due to the vertical movement of the piston tends to increase, but also when the inclination of the piston changes near the top dead center Since the outer periphery of the piston smoothly hits the inner peripheral wall of the cylinder and the impact is suppressed to a small level, the slap noise is also sufficiently suppressed. Further, the cross section at least at the maximum reaching height position of the overhang amount is a composite elliptical shape in which at least two ellipses having a major axis in the thrust / anti-thrust direction orthogonal to the pin boss axial direction and having different flatness ratios are combined. By making the part located on both sides of the major axis direction small flatness, and the part located closer to the pin boss than this part is a shape with high flatness, the deterioration of scuff resistance is prevented and the sliding resistance is more It is further reduced.
[0010]
In the present invention, it is preferable that the dimension in the height direction of the skirt portion is ½ or less of the piston diameter. Furthermore, it is preferable that the height direction dimension from the pin boss center height position to the skirt lower end is smaller than the height direction dimension from the pin boss center height position to the piston upper end.
[0011]
If this is done, the dimension in the height direction of the skirt portion will be reduced, which will reduce the contact area with the cylinder inner peripheral wall, which will be advantageous for reducing sliding resistance, while the inclination of the piston tends to increase. Thus, the slap noise is sufficiently suppressed by forming the outer shape of the skirt portion.
[0014]
The present invention is particularly effective when applied to an aluminum alloy cylinder block in which a piston is fitted. In other words, when the cylinder block is made of an aluminum alloy, the clearance between the outer periphery of the skirt and the inner wall of the cylinder increases due to the thermal expansion of the cylinder block when warm. However, according to the piston structure of the present invention as described above, the sliding resistance is sufficiently reduced even if the clearance is reduced so as to satisfy such a requirement.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 schematically shows a cross-sectional structure of a cylinder portion of an engine (internal combustion engine) to which the piston structure of the present invention is applied. In this figure, reference numeral 1 denotes a cylinder block constituting an engine cylinder, which is formed of, for example, an aluminum alloy.
[0017]
A piston 10 is fitted in a cylinder bore 2 provided in the cylinder block 1, and the piston 10 and the upper end (small end) of the connecting rod 3 are connected by a piston pin 4. In addition, a plurality of piston rings are fitted to the upper portion of the piston 10, and in the illustrated embodiment, the first and second compression rings 5A and 5B for maintaining airtightness and an oil ring 5C for scraping off oil are used. Three piston rigs are fitted. The lower end (large end) of the connecting rod 3 is connected to a crankshaft (not shown). A cylinder head 6 is installed above the cylinder block 1.
[0018]
2 and 3 show the piston 10 according to an embodiment of the present invention, and FIG. 4 schematically shows the piston 10 exaggerating the characteristic features of the present invention. As shown in these drawings, the piston 10 has an upper end piston head 11 and ring grooves 12A, 12B, and 12C for connecting the piston rings 5A, 5B, and 5C to the outer periphery thereof. The cylindrical portion having the skirt portion 13 and the pair of pin bosses 14 provided on both sides in the piston radial direction within the formation range of the skirt portion 13 are integrally provided and formed of an aluminum alloy or the like. The pin boss 14 has a pin hole 15 through which the piston pin 4 is inserted.
[0019]
The skirt portion 13 has a height direction dimension (skirt height H1) that is advantageous for reducing sliding resistance. For example, the skirt height H1 is set to ½ or less of the piston diameter D. ing. Furthermore, the height direction dimension H2 from the pin boss center height position to the skirt lower end is set smaller than the height direction dimension H3 from the pin boss center height position to the piston upper end. In addition, in order to reduce the height direction dimension H2 from the skirt height H1 and the pin boss center height position to the skirt lower end portion in this way, a working jig fitting enamel formed at the inner peripheral portion of the skirt lower end. 16 is shortened to the minimum necessary, for example, about 1 mm.
[0020]
The profile of the skirt portion 13 is shaped so that it gradually protrudes downward from the upper end of the skirt to the middle height, and gradually decreases from the middle height to the lower end of the skirt. It is a so-called barrel type, and has a shape as shown in FIG.
[0021]
That is, FIG. 5 shows the lower distance of the oil ring (distance from the upper end of the skirt) in the unit of mm and the vertical axis, while the amount of reduction in the major axis (1/2) is expressed in the unit of μm on the horizontal axis. Thus, the profile of the skirt portion enlarged in the major axis direction with respect to the height direction is shown. Here, the major axis reduction amount is an amount representing how much the major axis of each part of the skirt portion is smaller than the reference major axis, with the maximum value of the major axis of the skirt portion having an elliptical cross section as described below as a reference major axis. The major axis reduction amount becomes 0 at the maximum major axis (reference major axis), and the major axis reduction amount changes in the minus direction as the major axis becomes smaller.
[0022]
As shown in this figure, the amount of reduction in the major diameter gradually approaches 0 from the negative value as it goes downward from the upper end of the skirt to the predetermined height position near the lower end of the skirt, in other words, the overhang amount gradually increases. The overhang amount gradually increases further below the pin boss center height position B within the range of the skirt, and the overhang amount reaches a maximum value (the major axis reduction amount is 0). , Which is referred to as “maximum overhang amount reaching height position M”) is closer to the position L of the lower end of the skirt than the pin boss center height position B in the piston height direction , and the maximum overhang amount reaching height is reached. distance between the position M and the pin boss center height position B is, the overhanging amount maximum arrival height position M and outer shape of the skirt portion than the size Kunar such curved shape distance between the position L of the skirt lower end formed Has been. Here, the maximum overhang amount reaching height position M means the position of the upper end of the range when the portion where the overhang amount is maximized covers a certain range.
[0023]
As described above, the maximum overhang amount height position M is closer to the skirt lower end than the intermediate position between the pin boss center height position B and the skirt lower end position L within the range of the skirt portion. Compared to the conventional structure (indicated by a two-dot chain line in FIG. 5) where the reaching height position is close to the pin boss center height position, the skirt upper side overhang is suppressed. Note that chamfering is applied to a range of about 0.5 mm at the upper end of the skirt, and chamfering is also applied to a range of about 0.1 mm at the lower end of the skirt.
[0024]
In addition, the cross section at least at the maximum reach height position M of the skirt portion has a substantially elliptical shape having a major axis in the thrust / anti-thrust direction orthogonal to the pin boss axial direction. In this embodiment, the skirt portion has a height direction. The cross section is substantially elliptical throughout, and the dimension of the major axis is changed at each site in the height direction as described above (see FIG. 4).
[0025]
The cross-sectional shape of the skirt is particularly preferably a composite elliptical shape as shown in FIG. That is, FIG. 6 shows an exaggerated shape of the cross section of the skirt portion 13 (a shape in which the deviation between the major axis and the minor axis is enlarged). As shown in this figure, the outer shape of the cross section is at least two ellipses. The part 13a located on both sides in the major axis direction is composed of a part of the first ellipse E1 having a relatively small flatness, and the part 13b located closer to the pin boss than this part is the first part. It is composed of a part of a second ellipse E2 having a larger flatness than the ellipse E1. The first ellipse E1 has, for example, an ellipse amount (difference between major axis and minor axis) of about 430 μm.
[0026]
The operation of the piston structure of the present embodiment as described above will be described below.
[0027]
As shown in the schematic diagram of FIG. 4, when the piston 10 moves upward until the top dead center is reached in the compression stroke, the top of the piston 10 is tilted to the anti-thrust side (right side in FIG. 4). Further, when the piston 10 passes the top dead center and shifts to the expansion stroke, the piston 10 swings so that the top portion is inclined toward the thrust side (left side in FIG. 4) as indicated by an arrow in FIG.
[0028]
As a general tendency, since the piston speed is high during the stroke of the piston 10, the piston 10 slides on the oil film of the lubricating oil adhering to the inner peripheral surface of the cylinder, and the frictional force (sliding resistance) is reduced. In the vicinity of the point, since the piston speed becomes slow, the upper or lower part of the skirt portion 13 is pressed against the inner wall surface of the cylinder due to the inclination of the piston 10 toward the anti-thrust side or the thrust side as described above, and the oil film is easily cut. The frictional force tends to increase. Further, in the vicinity of the top dead center, a slap sound is generated when a part of the skirt portion 13 collides with the inner peripheral wall of the cylinder by the swinging motion of the piston 10 as described above.
[0029]
These tendencies occur not only near the compression top dead center but also near the intake top dead center.
[0030]
In contrast to these tendencies, in order to reduce the frictional force, the skirt part of the piston 10 has a rough shape compared to a so-called bell shape (constant cross-sectional shape from the vicinity of the upper end of the skirt part to the lower end part). The so-called barrel type is preferable because the contact area with the inner peripheral wall of the cylinder can be reduced. Further, the frictional force is reduced as the clearance between the piston 10 and the cylinder inner peripheral wall is increased. However, when the clearance is increased, the slap noise is easily increased. Accordingly, it is desired that the clearance between the skirt portion and the cylinder inner peripheral wall at the portion where the overhang amount is maximum is small enough to sufficiently suppress the slap noise. In particular, when the cylinder block is made of an aluminum alloy, the clearance increases due to the thermal expansion of the cylinder block when warm. Therefore, it is desired to make the designed clearance as small as possible.
[0031]
However, in the conventional barrel-shaped structure in which the projecting amount maximum reaching height position as shown by the two-dot chain line in FIG. 5 is close to the pin boss center height position, the frictional force reducing effect is impaired as the clearance is reduced. End up. On the other hand, according to the structure of the present invention, the frictional force reduction effect can be enhanced while sufficiently suppressing the slap noise. This effect will be described with reference to FIG.
[0032]
FIG. 7 shows a conventional barrel structure (profile indicated by a two-dot chain line in FIG. 5), which is small enough to sufficiently suppress the slap noise in the clearance between the skirt portion and the cylinder inner peripheral surface at the portion where the overhang is maximum. The value (about 14 μm) and the structure of this embodiment (profile shown by a solid line in FIG. 5), the clearance between the skirt portion and the cylinder inner peripheral surface at the portion with the maximum overhang is the same as the conventional barrel structure. The data obtained by measuring the change in the friction force during one cycle of the engine is shown for the equivalent, and the thick line is the data in the case of the structure of the present embodiment, and the thin line is the data in the case of the conventional barrel structure. In this figure, the upper side of the line where the frictional force is 0 (one-dot chain line) represents the frictional force generated when the piston is raised, and the lower side represents the frictional force generated when the piston is lowered.
[0033]
As shown in this figure, in the conventional barrel structure, the frictional force is immediately before and immediately after the compression top dead center (crank angle 360 °) and immediately before and after the intake top dead center (crank angle 0 °, 720 °). In contrast to this, in the structure of the present embodiment, the frictional force is increased by the amount indicated by hatching immediately before and immediately after the compression top dead center and immediately before and immediately after the intake top dead center as compared with the conventional barrel type structure. Reduced. The reason is considered as follows.
[0034]
When the piston is tilted toward the anti-thrust side or thrust side near the top dead center, if the skirt upper part overhangs, this part tends to press against the inner wall of the cylinder and the oil film breaks easily, and the skirt part is used to correct this tendency. However, the upper part of the skirt near the piston head is warmer than the lower part during operation and is thick. However, in the conventional structure in which the protruding amount maximum reaching height position is close to the pin boss center height position, the protruding due to the thermal expansion of the skirt upper portion cannot be sufficiently suppressed.
[0035]
On the other hand, according to the structure of this embodiment, the maximum overhang amount reaching height position M is closer to the position L of the skirt lower end than the pin boss center height position B in the piston height direction , and the overhang distance amounts up to reaching a height position M and the pin boss center height position B is set to the overhang amount maximum arrival height position M and the skirt lower end distance than the size Kunar such curved shape of the position L of As a result, the degree of suppression of the overhang of the skirt upper portion (reduction in the major axis) is increased, so that the overhang is sufficiently suppressed even when the skirt upper portion is largely thermally expanded during operation. As a result, the effect of reducing the frictional force in the vicinity of the top dead center is enhanced.
[0036]
On the other hand, the piston is easily tilted by suppressing the amount of overhang of the upper part of the skirt (reducing the major axis). Further, conventionally, in order to suppress the tilt of the piston, a downward extending portion is provided on the thrust side and the anti-thrust side of the skirt portion, or the entire skirt portion is formed long in the vertical direction. In this structure, in order to reduce the contact area with the inner wall of the cylinder so as to reduce the sliding resistance, the downward extending part is deleted and the entire skirt is shortened. The piston is easy to tilt.
[0037]
For this reason, there is a concern that the slap sound generated when the inclination of the piston changes before and after the top dead center is likely to increase. However, since the skirt outer shape has a smooth curved shape with gradually changing overhang, even when the piston tilt changes near the top dead center, the impact can be kept small by smoothly hitting the cylinder inner wall. Slap sound is sufficiently reduced. Even when the slap sound was actually measured, the slap sound hardly increased compared to the conventional case, and there was no generation of a slap sound at a level that would cause a problem in an actual vehicle.
[0038]
In this embodiment, in order to reduce the contact area with the cylinder inner peripheral wall and reduce the sliding resistance, the skirt portion is shortened as described above, and the cross section of the skirt portion is substantially elliptical. By adopting a composite elliptical shape as shown in FIG. 6, the sliding resistance is reduced while preventing the scuff resistance from deteriorating.
[0039]
In other words, the cross section of the skirt portion is substantially elliptical, and the contact area with the cylinder inner peripheral wall decreases as the flattening ratio increases. However, as the flattening ratio increases, the parts on both sides in the major axis direction that are contact parts with the cylinder inner peripheral wall Sharp points tend to cause scuffing (scratches due to partial seizure).
[0040]
On the other hand, when the cross section of the skirt portion is located on both sides in the major axis direction as in this embodiment, the flatness is small, and the portion located closer to the pin boss than this portion is a composite elliptical shape with a large flatness. The parts on both sides of the major axis in contact with the inner peripheral wall of the cylinder are not flattened, the scuff resistance is kept good, and the effect of reducing sliding resistance is enhanced by the large flatness of the part near the pin boss. It becomes.
[0041]
【The invention's effect】
As described above, the piston structure of the present invention has a so-called barrel-shaped skirt portion, and the overhang amount is a height position where the overhang amount gradually increases and reaches the maximum value as it goes downward from the upper end portion of the skirt. The maximum amount reaching height position is closer to the skirt lower end than the pin boss center height position in the piston height direction , and the overhang amount maximum reaching height position and the pin boss center height position are distance, because it forms a skirt portion outer to the size Kunar such curved shape than the distance between the projecting amount maximum arrival height position as that of the skirt lower end, the skirt upper large thermal expansion during operation However, the overhang of this portion can be sufficiently suppressed to reduce the sliding resistance, and the impact when the inclination of the piston changes near the top dead center can be suppressed to a small level.
[0042]
Therefore, it is possible to effectively achieve both improvement in fuel consumption and output performance due to reduction in sliding resistance and suppression of slap noise. Further, the cross section at least at the maximum reaching height position of the overhang amount is a composite elliptical shape in which at least two ellipses having a major axis in the thrust / anti-thrust direction orthogonal to the pin boss axial direction and having different flatness ratios are combined. By making the part located on both sides of the major axis direction small in flatness, and the part located closer to the pin boss than this part is in a shape with high flatness, sliding resistance is further improved while preventing deterioration of scuff resistance. It can be further reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a structure of a main part of an internal combustion engine to which a piston structure of the present invention is applied.
FIG. 2 is a front view of a piston in the piston structure of one embodiment of the present invention.
FIG. 3 is a cross-sectional view of the piston.
FIG. 4 is an explanatory view schematically showing the piston structure.
FIG. 5 is a view showing a profile of a skirt portion of a piston.
FIG. 6 is a diagram exaggeratingly showing a cross-sectional shape of a skirt portion of a piston.
FIG. 7 is a graph showing data obtained by measuring a change in friction force during one cycle of the engine in the case of the structure according to the embodiment of the present invention and the case of the conventional structure.
[Explanation of symbols]
1 Cylinder block 10 Piston 13 Skirt part 14 Pin boss H1 Skirt height D Piston diameter H1 Height direction dimension from pin boss center height position to skirt lower end part H2 Height direction dimension M from pin boss center height position to piston upper end part Maximum overhang height position B Pin boss center height position L Bottom skirt position

Claims (4)

The outer shape of the skirt part below the piston ring gradually protrudes from the piston ring side skirt top part to the middle height part as it goes downward, and gradually extends from the middle part to the skirt bottom part as it goes downward. Is a piston structure of an internal combustion engine in which is reduced,
As the skirt upper end moves downward, the overhang amount gradually increases and reaches the maximum value. The maximum overhang amount height position is higher than the pin boss center height position in the piston height direction. And the distance between the maximum extension height reaching position and the pin boss center height position is larger than the distance between the maximum extension height reaching position and the skirt bottom end position. to form a skirt portion outer in a curved shape such as Kunar,
In addition, the cross section at least at the maximum reach height position of the overhang amount has a composite elliptical shape in which at least two ellipses having a major axis in the thrust / anti-thrust direction orthogonal to the pin boss axis direction and having different flatness ratios are combined. A piston structure for an internal combustion engine, characterized in that a portion located on both sides of the major axis direction has a small flatness ratio, and a portion located closer to the pin boss than this portion has a large flatness ratio .   2. A piston structure for an internal combustion engine according to claim 1, wherein the height direction dimension of the skirt portion is ½ or less of the piston diameter.   3. A piston for an internal combustion engine according to claim 2, wherein the height direction dimension from the pin boss center height position to the lower end of the skirt is smaller than the height direction dimension from the pin boss center height position to the piston upper end. Construction. The piston structure for an internal combustion engine according to any one of claims 1 to 3, wherein a piston is fitted into a cylinder block made of aluminum alloy.

Images